During an idling situation, i.e. a situation where there is no power production, wind turbines usually have a fixed pitch position, depending on the wind speed, which is maintained constant for a constant wind speed.
Typically said pitch position is around 70° for low wind speeds and close to 90° for high wind speeds, for allowing a slow rotor rotation which helps for the lubrication of the drivetrain, specially the gearbox.
In idling situations above the cut-out wind speed Vout which determines the stop of the power production, a position of the blades close to the feather position involves large loads in the wind turbine, especially in the blades and/or the tower. These large loads can have an important unsteady component, which can contribute significantly to fatigue and/or extreme loads.
In some critical wind farm sites, the long-term wind distribution (usually defined with a Weibull probability distribution) causes that the wind turbine is in an idling situation above Vout during an important part of its lifetime. In that case the loads provoked in those idling situations can contribute importantly to the overall loads level of the turbine.
For instance, in those wind farms with a Weibull shape factor k close to 3 the wind turbine is in an idling situation above Vout during a lot of time making, in that case, the lateral fatigue load Mx in the tower even larger than the longitudinal component My. This is certainly unusual, since the longitudinal component My of the tower fatigue load is usually larger than the lateral component Mx in most of wind farms.
The present invention focuses on finding a solution for these drawbacks.